Electric ship propulsion.



W. L. R. EMMET.

ELECTRIC SHIP PROPULSION.

APPLICATION FLLED JULY 23. $915- 1 ,290,94:5, Patented Jan. 14, 1919.

Inventor Vvilliam LR mmet Hlsu t or'neg.

shah.

it) is ENECTADY. NE'W' YORK-l1, ASSIGNOR TC GENERAL WILLIAM L. EIVIMET. OF Sci-.

ELECTRIC COMPAN A COEPGBATION D5 IJE'W YDRK EEECTLRIC SHIP PROPULSION.

Application filed July 1915.

To (:(Z IU/Lt/J/L may concern:

Be it known that l, lVILnLur L. R. EM- )nrr. a citizen of the United States, residing at. t-lchcncctzuli'. county of Schenectady, State of Non York, have invented certain non and useful lin movements in Electric vShip Pro sion, of which the following is Li ation. lty .iuvtmtion relates to clot pulsion and in particular-to ll of slii by alternating curl motors. The object of y invention is to provide a novel and improved arrangement, of appmitns for minimum of apparatus. A further object of my invention is to provide inipro red apparatus for operating an electrically propelled ship at full and maneuvering speeds in a more simple, satisfactory and cliicient. manner than has heretofore been done. Other objects of my invention will he apparent from the following: description and appended claims.

The features which i believe to be patentably characteristic of my invention are dolinitely indicated in the claims appended hereto. The methods of operating an cloctrically propelled ship and the novel and improved arrangements of apparatus for carrying out these methods, in accordaiu-e with my present invention, will be understood tron. the following description taken in connection with the aecoirqntnyinp drawings in whit-hr Figure. 1 illustrates dia n'ainniatically a system of electric ship propulsion embodying the features of my present invention; Fig. 2 is a detail View of the secondary wind ing of the motor shown in the system at Fig. l; and is a detail View of a modified type of secondary Winding.

[i cm oi ship propulsion generall consists oi three eleinents.,'(l a main motive means or prime-hover, such as a steam engine or elastic lluid turbine, a propeller shaft and (3) a spec-d 'ng' mechanism reduci for securing the desired speed ratio:-; hotiveen the mime-mover and the propeller shaft. in an electrically propelled ship. the speed reducing mechanism taltcs the form o't an eh "ic generator driven in the prime mover and supplying: electric energy to an electric motor cmmected to the propeller The use of alternating: current is very desirable in electrically propelled ships,

Specification of Letters Patent.

operating ships "with areversing torque must be available.

Patented Jan. 14:, 1919.

Serial no. 33,507.

since alternating current generators and motors are simpler than corresponding direct current machines, and the generators can be conveniently. designed for larger capacities and higher speeds, and are, therefore, better adapted for use with steam turbines. Alternating current induction motors are also desirable, sincc'they can be constructed and Wound to Withstand the roughest usage with a minimum amount of trouble and eX- pense for maintenance.

A ship-is usually run at one particular speed during'ihe greater part of the time its propelling apparatus is in use, and in most cases it is only when maneuvering in harbors or about ivharves that diflerent. speeds are used. The power required to drive a ship varies substantially as the cube of the ships speed. The maximum power required for running at full speed ahead is, therefore, very considerably greater than the power require for lower navigating speeds. The resistance oll'ercd by the Water to a propeller is substantially constant for any particular speed of the ship, and, accordingly, the power required to drive the ship is subtantially constant for any particular ships speed. lhc normal starting of the ship in either direction from a condition of rest does not require much power or the application of a relatively large torque, since the speed, and hence the required power, increase gradually from their respective initial or.

ininin'iurn values. Where alternating current is used, start ng can be very effectively accomplished by bringing the propeller-driving motors and. the alternating current grencrator up to speed together. Thus, little or no ditliculty ordinarily encountered in bringing a ship from stand-stillup to and in maintaining cruising or full running speeds ahead. in maneuvering and particularly in reversing very exacting and abnormal demands are apparatus. For example, Where a ship must he suddenly reversed. or even stopped, when running}; at full speed ahead, a very large And again, in maneuvering'in harbors and around Wharves a large torque is frequently required for quickly reversing the direction of motion of the ship. The most exacting; and difir-ult maneuver is obviously the reversal, or even the stopping. of the. ship after full speed it a ship is running at full speed ahead .ia-de upon the propelling";

and the application of power to a propeller shaft is stopped, the propeller Will continue t e-spin around in the reverse direction, due to the motion of the ship. In order to reverse the direction of rotation of the propeller, a torque must be applied to its shaft sutliciently great to break the propeller away from the Water. if the reversing torque is not large enough to break the propeller away from the water, the propeller will merely Continue to spin around in response to the motion of the ship, while the ship will slow down very gradually, and the propeller will not break away from the water until the torque, due to the motion of thev ship, becomes smaller than the reversing torque. li hen once the propeller has been broken away from the water, its reversal apparently becomes easier, and the ship can then be brought to rest and started in the reverse direction. Thus, a very high speed of the propellers in the reverse direction is not practicable until the ship has been brought to rest and given a high speed in the reverse direction, so that the real need of reversing is not the ability to produce high propeller speed but the ability to produce high torque with a reduced propeller speed.

The torque of an induction motor for a given generator output is increased by increasing the number of primary poles, since increasing the pole number of the primary winding of the motor corresponds to increasing the speed reduction between the primemover and the propeller shaft. The torque of an induction motor may also be incr used by increasing the resistance losses in the secondary winding, but since high torque so obtained means large secondary losses, eii'iciency must generally be sacrificed where high torque is desired. For running a ship at full speed ahead the maximum power is required, and it is essential that the propeller-driving motors should then operate at high efficiency. The maneuvering operations of a ship last for relatively very short intervals of time, and it is not required that the propelling a )paratus be economically operated during these brief intervals. It will thus be seen that efficiency may well be sacrificed to secure high torque during the brief intervals of maneuvering, provided the propeller-driving motors operate with high eiiicicncy at full speed. lvly present invention contemplates the provision of a novel and improved method of and apparatus for operating an electrically pro pelled ship withhigh etliciency at full runniing speeds ahead and with high torque for reversing the direction of motion of the ship.

My present system of propulsion comprises a suitably driven alternating current generator supplying energy to an induction mo est motor having its rotor mounted 'on the propeller shaft. As is well known, the speed ratio between such a generator and motor can be changed by changing the number of poles of the primary winding of the motor. The induction motor of my present system has a primary winding, or windings, adapted to produce magnetic fields of two diiierent pole numbers, and in its preferred form is provided with means whereby an increased torque is produced when the primary winding is arranged for reversing. This increased torque can be produced by employing a. secondary winding affording a low resistance path for the secondary current for the high speed polo number and a relatively high resistance path for the low speed pole number. Numerous constructions and arrangements of secondary windings possessing such characteristics will suggest themselves to those skilled in the art, such for example as a secondary Winding so connected to an external resistance that the resistance is inactive for the high speed .pole number and active for the low speed pole number. or a secondary Winding of which one component is of low resistance and the other of relatively high resistance, the low resistance component being in effect substantially open-circuited for the low speed pole number. An increased torque for reversing may also be obtained by using an induction motor designed to have a secondary circuitof relatively high efi'cctive resistance at large slips of the. motor. In the broadest aspect of my invention. pole-clmnging alone may be cmployed for rcversmg. My method of operat mg this system consists in connecting the primary winding for its high speed pole number for running the ship at full speed ahead and for its low speed pole number for reversing the direction of motion of the ship.

I am aware that. polechanging has heretofore been used to obtain dilicront speeds of an induction motor, but I believeI am the first to employ polo-changing in a system of electric ship propulsion for the purpose of obtaining an increased motor torque for reversing the direction of motion of the ship. As previously explained, the torque of an induction motor, for a given generator output, is increased by increasing the number of primary poles because the motor speed is thereby decreased. This will be understood by remen'ibcring that the generator and motor act as a speed reducing mechanism between the prime-mover and the propeller shaft. In accordance with my present method of operation, the generator output is, for the purpose of reversal. utilized at a lower propeller speed, whereby the propeller-driving torque is increased.

Referring now to Fig. 1 of the drawing there is diagranunatically represented an elastic fluid turbine 10 mechanically coupled to a polyphase alternator. I have shown for the purpose of illustration an alternator of the revolving field type having an exciting winding 11 supplied with direct current from any suitable source 132 by means oil slip rings 13 and cooperating brushes. The alternator has a polyphase stator winding 1-l connected to bus bars 15 or the like. The propeller 16 is mounted on the same shaft .17 as the rotor 18 of an induction motor. In the drawings, 1 have illustrated the secondary-winding of the motor carried by the rotor member and the primary winding as mounted in the stator lllillllbfil, but it will of course be understood that the primary wind ing may be carried by the rotor member, in which case the secondary winding will be incorporated in the stator member.

The primary winding '20 of the motor adapted to be arranged for a plurality oi": different pole numbers. To this end an of the Well known means for producing primary magnetic poles of different pole num bers may be employed, and since there are numero arrangements for effecting this purpose I do not deem it necessary to explain in detail any specific means, but by way of example, I will mention a patent of Ernst F. Alexanderson No. 841,609, dated January 15, 1907 as illust ating one way in which the primary winding 20 may be arranged to produce primary magnetic poles of different pole numbers. F or the purpose of explaining my invention. I have illustrated a polechanging switch 21 connected to the primary winding 20 by six leads 2? and to the bus bars 15 by three leads This diagrammatic representation of a primary winding adapted for pole-changing will be well understood by those skilled in the art. reversing switch '24: associated with the leads 23 and serves to reverse the phase rotation between the magnetic field of the alternator and that or" the motor in the wellundcrstood manner. A switch is also provided for disconnecting the motor "from the bus bars.

The pole-changing switch 21 chan es the speed ratio of the motor with respect to the frequency of the alternator. The relative values of these speed ratios will be determined by the particular conditions to he met, such as the desired full speed of the ship, and the magnitude of the reversing torque required for such a ship. The higher speed ratio employed for manning" the ship at full sped ahead while the lower speed rati. is employed for reversing the direction of motion of the ship. i believe it will I(.;itlall) be found necessar} to provide means. for accentuatine motor to cue for the lower sped ratio. This can be advantageously done by prtwiding; a secondary wind ing which has low resistance for the high speed pole number and relatively high resistance for the low speed pole number of the primary winding. Merely for the purposes of explanation I have in the accompanying drawings illustartcd a compound or double secondary windin ()nc winding is made up oi relatively high resistance eonductorbars 37 connected at their ends to end rings 26 to form. a squirrel cage Winding o'l relatively high resistance. This Winding is ob'viouslv cll'e tive for any pole number oi the primary windin The other winding is a definite winding and consists of low resistance conductor bars 27 having end connectors I connecting: the bars as a polar winding. Che end connectors are so designed that the pitch of the conductor bars 27 is substantially 100 per cent. when the primary winding is arranged for its high speed pole number and in the neighborhood of 200 per cent. when the primarv winding is arranged for its low speed pole number. 'lhusfthc conductor bars 2? form a ow resistance path for the secondary current when the primary winding is arranged for the high speed ratio, and are substantially open-circuited when the primar) winding" is arranged for the low speed ratio.

The torque of the propeller driving induction motor may also be advantageously accentuated by employing a secondary Winding of inductively changing effective resistance, that is to say a secondary winding whose effective resistance inductively changes, so that the effective resistance varies as a direct function of the frequency of the secondary current. Such a winding has relatively high effective re istance when the secondary current is of high. frequency and relatively low effective resistance when the secondary current is of low frequency. Numerous constructions and arrangements for obtaining a secondary winding having an inductively changing eiiectivc resistance are known in the art, and I have merely for the purposes of illustration, shown in Fig. 3 of the accompanying drawings a. double squirrel cage winding. The conductor bars of one of these squirrel cage windings are ex? low resistance and are positioned in well beneath the surface of the magnetic core of the rotor, and since these con ductor bars are substantially embedded in magnetic material. the winding as a whole has high inductance. ihe conductor bars 3 o? the other squirrel cage whaling have relatively high ohmic resistance and are located in slots nea the surface of the magnetic core oi the rotor, and. thus, this winding as a whole has little iiuluctaiuzc. On ac count of its high sclt-inductiom the low 1 istance winding arries very little current when the frequency oi the secondary current is high, and consequently under this condition the secondary current is forced to flow through the conductors 31 of the high resistance winding. As the frequency of tie secondary current diminishes, more and more current flows through the low resistance winding, until at normal slip the motor has the desirable running characteristics oi an induction motor with an ordinary squirrel cage secondary winding. In the act oi": reversal, the direction of rotation of the primary magnetic field of the propeller driving motor is reversed. At the instance of reversal, after full speed ahead, the slip of the motor is abnormally high, because the rotor is revolving in the opposite direction to the primary magnetic field, and the secondary current is hence of relatively high frequency, being in fact nearly double the frequency of the primary current. The secondary winding, therefore, has a relatively highefi'ective resistance, Which. it retains until the ship has been reversed and the slip of the motor reaches its normally small value.

The arrangement of apparatus in accord ance with my present invention is capable of giving an increased torque in reversing with lighter apparatus and better power factor under normal operating conditions than in any similar system with which I am acquainted. The propeller-driving motor in my present system has a secondary winding of low resistance when the motor is connected for running the ship full speed ahead, and the efi'iciency oi": the motor for this condition of navigation will, accordingly, be high. lVhen connections for reversal are made the pole number of the primary winding is increased, thereby in creasing the torque available with the generator output, and the secondary losses are simultaneously increased, due to the in creased effective resistance of the secondary winding for reversing purposes whereby the required reversing torque is produced. The pole-changing arrangement and increased effective resistance of the secondary vi'inding of the motor thus produces a sa factory reversing torque with little or no distortion of the normal operating characteristics of the motor.

VVhile I have shown a single motor connected to one propeller shaft, will be obvious that a ship may. and usually will. have more than one propeller. My present invention is concerned with the arrangement of apparatus for operating a propeller driving induction motor, preferably possessing certain particular characteristics, whether or not such motor is used alone or in combination with the same or other forms of motors. I do not. therefore, wish to be restricted to the particular arrangement of apparatus herein illustrated and described for the purpose of explaining the principleoi my invention, but I aim in the appended claims to cover all modifications within the spirit and. scope of invention.

vi hat 1 claim as new and desire to secure by Letters nt of the United States, is

1. A system comprising a propeller an induction motor adaptcthto drive said propeller said motor having a primary winding adapted o"produce primary magnetic fields of di. rent pole numbers, two secondary windings one of which serves as means for developing a motor torque for running the ship full speed ahead when the primary winding is connected to produce a relatively low numher of poles and the other as means for in creasing the motor torque for reversing the direction motion of the ship when the number oi? primary magnetic poles is increased, said secondary windings being connected and arranged so that the secondary resistance losses of the motor are increased when the number of primary magnetic poles is increased, and means for connecting said primary winding to produce the lower number of poles for normal continuous operation of the ship and for producing the higher number of poles when reversing the direction of motion of the ship.

2. A system of electric ship propulsion comprising a propeller, an induction motor adapted to drive said propeller said motor having a primary winding adapted to produce primary magnetic fields oi two different pole numbers and secondary winding; having one portion of relatively high tive resistance for the higher numher of primary poles and another portion of low effecti resistance for the lower number of primary poles, and means for connecting said primary winding to produce the lower number of poles for normal continuous opof electric ship PTO-{misled era-tion of the shin and to p oduce the higher number of poles ror reversing the direction of motion of the ship.

repulsion 3. A system of electric ship p:

comprising a propeller, an induction motor eration of the ship and to produce the higher numberof poles for reversing the direction of motion of the ship.

4.. A system of electric ship propulsion comprising a propeller. an induction motor adapted to drive said propeller said motor naeogiea having a primary winding adapted to produce primary magnetic fields of two difiercnt pole numbers and secondary conductors a portion of which provides a relatively high resistance path for the secondary cur rent with the higher number oi primary poles, the other portion remaining inactive; said other portion being so pitched as to become active and form a low resistance path for the secondary current with the lower number of primary poles, and means for developing a motor torque for normal continuous operation of the ship by connecting the primary Winding to produce the lower number of poles and for increasing the motor torque for reversing the direction of motion of the ship by connecting the primary Winding to produce the higher number of poles.

5. A system of electri ship propulsion comprising a propeller, an induction motor adapted to drive said propeller, said motor having a primary winding adapted to produce primary magnetic fields of two ditferent pole numbers and two secondary windings one of which is a relatively high resistance squirrel cage Winding and the other a low resistance definite winding for the lower number of primary poles which bccomes a substantially open-circuited winding for the higher number of primary poles, and: means for connecting said primary winding to produce the lower number of poles for normal continuous operation of the ship and for connecting the primary winding to produce the higher number of poles to increase the motor torque for reversing the direction of motion of the ship.

6. A system of electric ship propulsion comprising a propeller, an lnduction motor adapted to drive said propeller, said motor having a primary winding adapted to produce primary magnetic fields of two difl'ercnt pole numbers and a secondary winding arranged to have one portion yield low eft'cctive resistance for the high speed pole number and relatively high efi'ective resist ance for the low speed pole number of the primary winding, the other portion 'being a squirrel cage winding, and means for connecting said primary winding for its high speed pole number fornormal continuous operation of the ship and for its low speed pole number for reversing the direction of motion of the ship.

7. A system of electric ship propulsion comprising-a propeller, a single induction motor adapted to drive said propeller, said motor having a primary winding adapted to produce primary magnetic fields of two difterent pole numbers and a secondary winding having a portion arranged to be inactive for the high pole number and to be actively included in circuit with the other portion of the secondary winding of the motor for the low pole number of the primary winding, and means for connecting said primary winding for its high. speed pole number for normal continuous operation of the ship and for its low speed pole number for reversing the direction of motion of the ship.

In witness whereof, I have hereunto set my hand this 7th day of July, 1915.

VVILLIAM L. R. EMMET. 

